Abstract
Nitrogen (N) and irrigation water must be effectively used in mineral soils to produce carrots with high yield and minimal environmental impact. This study attempts to identify optimal N and irrigation management practices for low desert carrot production in California by investigating consumptive water use and N uptake and removal rates in fresh market and processing carrots. Field experiments were conducted at the University of California Desert Research and Extension Center and nine farmer fields during two growing seasons. The actual evapotranspiration (ETa) was measured using the residual energy balance method with a combination of surface renewal and eddy covariance equipment. Crop canopy coverage, actual soil nitrate-N from multiple depths as well as total N percentage, dry matter, and fresh biomass in roots and tops were measured over the growing seasons. The length of the crop season had a wide range amongst the experimental sites: from a 128-day period in a processing carrot field to as long as 193 days in a fresh market carrot field. The seasonal ETa varied between 305.8 mm at a silty loam furrow irrigated processing carrot field and 486.2 mm at a sandy clay loam sprinkler irrigated fresh market field. The total N accumulated at harvest ranged between 205.4 kg ha−1 (nearly 52% in roots) and 350.5 kg ha−1 (nearly 64% in roots). While the mean value of nitrogen removed by carrot roots varied from 1.24 to 1.73 kg N/Mg carrot roots, it appears that more N was applied than was removed by carrot roots at all sites. Within the range of N application rates examined at the experimental sites, there was no significant relationship between carrot fresh root yield and N application rate, although the results suggested a positive effect of N application on carrot yield. Sufficient soil N availability over the growing season and the lack of significant yield response to N application illuminated that optimal N rates are likely less than the total amounts of N applied at most sites.
Highlights
Carrots (Daucus carota L.) are one of the major commodities in the low desert of California, with an average planted area of nearly 8500 hectares over the past decade [1]
Carrot roots are vulnerable to forking, which can be caused by over-applying N fertilizer [2]
Since the primary focus of this study was the California low desert region, field experiments were conducted at the University of California Desert Research and Extension Center (DREC) and nine commercial fields in this region
Summary
Carrots (Daucus carota L.) are one of the major commodities in the low desert of California, with an average planted area of nearly 8500 hectares over the past decade [1]. Carrot is a cool-season crop that demands specific growing conditions and an adequate supply of mineral N and water for successful commercial production. Optimizing nitrogen and water management in carrot production is crucial for maximizing crop productivity and minimizing costs and nitrate leaching losses. Appropriate soil fertility and uniform soil water availability are critical for good root formation [1,2]. Carrot roots are vulnerable to forking, which can be caused by over-applying N fertilizer [2]. Excessive watering increases the incidence of hairy roots, discourages good color formation, and may encourage disease incidence [3]. Severe drying and wetting cycles result in the significant splitting of roots
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